From our first look at the data, the difference between Master’s and PhD in
the management group is different than in the non-management group.
This is an interaction between the two qualitative variables management, M
and education,E. We can visualize this by first removing the effect of
experience, then plotting the means within each of the 6 groups
using interaction.plot.

In [128]: try: .....:kidney_table=pandas.read_table('./kidney.table') .....:except: .....:url='http://stats191.stanford.edu/data/kidney.table' .....:#the next line is not necessary with recent version of pandas .....:url=urlopen(url) .....:kidney_table=pandas.read_table(url,delimiter=" *") .....: